Odd first forum post. Not much of a forum posting person, but I couldn't resist this one.
My worst was a Macanudo Maduro Hampton Court (Tubo). I expected a decent medium grade cigar; it was Macanudo after all. Not exactly yellow Cohiba, but a solid name nonetheless.
I cut it and the draw was very very tight. I was sucking as hard as I physically could, and got barely any air through. So I cut it further...no change. Twice more I moved up hoping to gain some draw with no luck. To its credit I was well past the cap and it didn't unravel. So it had that going for it.
At that point I figured I'd just have to hope I was capable of sucking a golf ball through a garden hose and lit it. I gave it all my might and was rewarded with a flavor I can only describe as mushrooms so rotten they could grow other mushrooms on top of them, with a distinct undertone of swamp.
I was pretty determined to have a decent smoke, so I kept on anyway hoping the flavor would change quickly. I smoked about a quarter inch of it before I finally admitted defeat, cut off the cherry, and chucked it as far into the woods as I could. I felt like Swamp Thing had just blown a load in my mouth, and went inside and gargled Listerine and generally felt dirty for a few minutes.
I don't know if the B&M I got it from had just kept it at 90% humidity until the insides were rotten, or if that's what those normally taste like...but I've never been brave enough to get another to find out. That, gents, was the worst cigar I ever had.